There is an underground Roman-era quarry in The Netherlands that, when you exit, you will find that you have crossed an invisible international border somewhere down there in the darkness, and that you are now stepping out into Belgium; or perhaps it's the other way around, that there is an underground Roman-era quarry in Belgium that, when you exit, you will find that you have crossed an invisible international border somewhere down there in the darkness, and that you are now stepping out into The Netherlands.

However, this is not just a disused quarry—not just an archaeological site on the fringes of the Roman empire that was once mined for blocks of limestone. Its afterlife is by far the most interesting part of the story.

For nearly a century, beginning in the 1800s, these underground hollows were used by Jesuit monks as a secluded place for prayer, study, and meditation, and even for the carving of elaborate and impressive forms into the soft rock walls; then the Nazis took over, transforming this weird underworld into a subterranean factory for World War II airplane parts; then, finally, pushing the stakes yet higher, the whole complex of former Roman limestone mines, straddling an international border underground between two modern European nations, was turned into a doomsday bunker for NATO, a dark and mold-prone labyrinth within which military commanders constructed a Joint Operations Center for responding to the end of the world (whenever the time finally came).

"There was even a 3-hole golf course complete with artificial turf," Subterranean Britannica reports in a recent issue of their excellent magazine, Subterranea.

"The complex was on average 50 meters below ground covering an area of approximately 6750 acres with eight miles of corridors, 400 branches and 399 individual offices," SubBrit explains. There were escape tunnels, as well, "one going out to the banks of the Albert Canal in Belgium, and one which came out in a farmer's potato store in the village of Kanne." It had its own water supply and even a dedicated wine cellar for NATO officers, who might need a glass of Europe's finest chardonnay to help feel calm enough to launch those missiles.

Just look at this thing's mind-boggling floor plan.

The "streets" were named, but not always easy to follow; however, this didn't stop officers stationed there from occasionally going out to explore the older tunnels at night. A former employee named Bob Hankinson describes how he used to navigate:

Most corners were roughly 90 degrees, but only roughly. Going through the caves was an exercise in left and right turns every 50 feet or so. Navigation was helped by street names. Unlike in the USA, where streets are numbered on a sort of grid pattern, these were zigzag streets. My office on Main Street and J Street, so if I got lost I would just keep walking until I came to either Main or J, and join it. If I went the wrong way, eventually the street would peter out either at the perimeter or a T-junction, and you would just turn round and go back the other way.

As another former employee—a man named Alan Francis—explains, "If I did have spare time, I would wander through the dark tunnels where there were very few lights on at night, thinking how strange it was to be working in a Roman stone quarry."

Writing in Subterranea, SubBrit explains that "nothing ever came out." This was "a strict rule: apart from people, anything that went in never came out. All waste material ranging from redundant furniture to foot waste was dumped in one of the sixteen underground landfill sites" designated within this sprawling whorl of rooms and passages. Shredded documents were even mixed with water and applied directly to the walls as a kind of fibrous paste, used for insulation.

Such was the secrecy surrounding this place that it was officially classified as "a 'forbidden place' under the Protection of State Secrets Act which forbade people to even talk about it."

One reason why the underground galleries are so vast, meanwhile, is apparently because of the character of the limestone they were carved through; in fact, "the limestone was so soft that the workers used a chainsaw to cut it."

The notion that I could just cut myself a whole new room with a chainsaw—just revving this thing up and carving an entire new hallway or corridor, pushing relentlessly forward into what looks like solid earth, possibly even sawing my way into the roots of another country—is so awesome an architectural condition that I would move there tomorrow if I could.

Just imagine building this titanic doorway into the earth with a small group of friends, a case of beer, and a few chainsaws. It's like Cappadocia by way of the Cold War. By way of Husqvarna.

Sadly, the whole place is contaminated with asbestos and has been badly saturated with diesel fuel. At least one environmental analysis of the underground maze found that "diesel fuel from the [copious emergency fuel] tanks had leaked into the porous limestone over a long period and had penetrated to a depth of about forty feet into the rock."

You can imagine the weird bonfires that could have resulted should someone have been stupid enough to light a match, but "this area had to be removed and disposed of," we read—presumably by chainsaw.

Nonetheless, today you can actually take a tour of this place—this now-derelict doomsday logistics hub that straddles international borders underground—courtesy of the Limburg Landscape Foundation.

If you can take the tour, let me know how it goes; I'd love to visit this place in person someday and would be thrilled to see any photographs.